1. Field of the Invention
The present invention generally relates to a nonvolatile memory, in particular, to a 2-cells-per-bit nonvolatile memory structure.
2. Description of Related Art
Nonvolatile memory is widely applied in various electrical apparatus because it can retain information even no power is supplied thereto. According to the limit of programming times, nonvolatile memory is divided into multi-time programmable (MTP) memory and one-time programmable (OTP) memory. MTP is multi-readable and multi-writable. In general, MTP has a single charge storage region for writing and reading information (i.e. 1 cell/bit).
However, as the development of memory structure, the gate oxide under the charge storage region of MTP becomes too thin, and thus the data retention capability may deteriorate when defects occur in the gate oxide. Therefore, there is a need in this industry to improve the data retention characteristics of the nonvolatile memory.